The present invention pertains to multiple-beam klystrons.
Multiple-beam klystrons are well-known in the prior art. The principle and structure of these klystrons will be recalled in the description of FIGS. 1 and 2.
A great advantage of these klystrons is that they are especially well suited to high-powered operations.
For it can be shown, that for one and the same high-frequency power, the acceleration voltage applied between the anode and a cathode of the klystron is far weaker in a multiple-beam klystron than in a single-beam klystron. Now, regardless of the type of klystron, the need to modulate the speed of the electron beam imposes one and the same upper limit on this acceleration voltage, beyond which the beam can no longer be modulated. Consequently, with a multiple-beam klystron, it is possible to obtain far greater high-frequency power than with a single-beam klystron.
The problem that arises is that it is not possible, with multiple-beam klystrons of the prior art, to obtain high power values at high frequencies.
For, at high frequencies, the dimensions of klystrons become very small. Limits are then imposed by the dimensions of the drift tubes of the cavities, the holes of which must be big enough to allow an electron beam to pass through, and the density of this electron beam should not reach a prohibitive level, all the more so as high power values are sought to be obtained.
In practice, problems arise when it is sought to produce power values of several tens of megawatts at frequencies of several thousands of megahertz.